Preparation Of Stabilized Fe~0 Nanoparticles Nanometer For Hexavalent Chromium Removal From Soil

Soil is the most important source for human beings, which paly an irreplaceable role in people’s life and production. However, with the rapid development of industry and economy, chromium compounds are widely used in various industries(e.g., metal electroplating, electronic, tanneries, metallurgy and wood preserving). So large quantities of Cr(VI) have been discharged into the environment due to improper disposal and leakage. The large toxicity of Cr(VI) led to a series of negative effects, affecting around animals, plants and human health. Much concern has been paid on the technology for Cr(VI) contamination remediation.Recently research showed that nanoscale zero-valent iron material has become a very active research field among the current environmental pollution remediation technologies for its high reactivity of repairing various environmental pollutants. But in practice application, there are still some problems need to be solved for nanoscale zero-valent iron material, such as synthesis condition of iron nanoparticles is not easy to control. Iron nanoparticles are easy to reunite and poor air stability. All of these factors put forward severe challenges on the preparation of nanometer iron material and use.In the present paper, stabilized Fe0 nanoparticles were synthesized by reduction of ferrous sulfate using sodium borohydride by applying polyvinylpyrrolidone(PVP) and carboxymethyl cellulose(CMC) as stabilizer. This paper studied the stability of the stabilized Fe0 nanoparticles, evaluated the capacity of stabilized Fe0 nanoparticles to remove Cr(VI) form soil, and discussed the kinetics and removal mechanisms of Cr(VI) by stabilized Fe0 nanoparticles. The results are as following:1. The optimized conditions for preparation of PVP-stabilized Fe0 nanoparticles were: the additive amount of PVP 0.5 g, the additive amount of ethanol 20 m L and the molar ratio of Fe SO4?7H2O and Na BH4 1:3. The PVP-stabilized Fe0 nanoparticles prepared under these conditions have high reactivity. The results of characterization showed that the average size of PVP-stabilized Fe0 nanoparticles was 50–100 nm. The BET surface area of nano zero-valent iron was 53 m2/g. The results of single factor experiment showed the higher removal efficiency of Cr(VI) in soil under the conditions of the higher PVP-stabilized Fe0 nanoparticles dosing quantity(0.4 g/L), the lower initial concentration of hexavalent chromium in soil(138.93 mg/kg), the lower p H value(3). Orthogonal experiment was conducted according to the results of single factor experiments. The optimal conditions were as follows: PVP-stabilized Fe0 nanoparticles dosing quantity 0.3 g/L; initial concentration of hexavalent chromium in soil 138.93 mg/kg; the p H value 5. The reaction kinetics of PVP-stabilized Fe0 nanoparticles with Cr(VI) was pseudo-first order reaction. The apparent rate constant kobs was 0.0093 min-1. Eh-p H thermodynamic diagrams were used to explain the removal mechanisms of Cr(VI) by nano zero-valent iron. Under the acid condition, the prevailing form for Fe was Fe2+ and for Cr were Cr3+ and HCr O4-. The hexavalent chromium was easy to be reducted to trivalent chromium, the removal rate of hexavalent chromium in soil was high. Under the alkaline condition, the prevailing forms were Cr(OH)2+、Cr(OH)2+、Cr(OH)3、Cr(OH)4- and Fe(OH)3, as well as the form of co-precipitation, which lead to low removal rate of hexavalent chromium in soil.2. The optimized conditions for preparation of CMC-stabilized Fe0 nanoparticles were: the mass ratio of CMC 0.2%, the additive amount of CMC 20 m L and the molar ratio of Fe SO4?7H2O and Na BH4 1:3. The CMC-stabilized Fe0 nanoparticles prepared under these conditions have high reactivity. The results of characterization showed that the average size of CMC-stabilized Fe0 nanoparticles was 80–100 nm. The BET surface area of nano zero-valent iron was 16 m2/g. The results of single factor experiment showed the higher removal efficiency of Cr(VI) in soil under the conditions of the higher CMC-stabilized Fe0 nanoparticles dosing quantity(0.6 g/L), the lower initial concentration of hexavalent chromium in soil(138.93 mg/kg), the lower p H value(3). Orthogonal experiment was conducted according to the results of single factor experiments. The optimal conditions were as follows: CMC-stabilized Fe0 nanoparticles dosing quantity 0.5 g/L; initial concentration of hexavalent chromium in soil 138.93 mg/kg; the p H value 5. The reaction kinetics of CMC-stabilized Fe0 nanoparticles with Cr(VI) was pseudo-second order reaction. The apparent rate constant kobs was 0.0004 min-1. Eh-p H thermodynamic diagrams were used to explain the removal mechanisms of Cr(VI) by nano zero-valent iron. Under the acid condition, the prevailing form for Fe was Fe2+ and for Cr were Cr3+ and HCr O4-. The hexavalent chromium was easy to be reducted to trivalent chromium, the removal rate of hexavalent chromium in soil was high. Under the alkaline condition,the prevailing forms were Cr(OH)2+、Cr(OH)2+、Cr(OH)3、Cr(OH)4- and Fe(OH)3, as well as the form of co-precipitation, which lead to low removal rate of hexavalent chromium in soil.